A resonator has a frequency response in which a sharp peak at a specific frequency appears in the amplitude of its transfer function. The high gain at a specific frequency makes a resonator useful for a sigma-delta type analog to digital converter (ADC). How to design resonators using an opamp or opamps has been proposed in applications for sigma-delta type ADCs. The speed at which these types of ADCs can work is determined mostly by the bandwidth of those resonators, which is in turn the bandwidth of opamps in the resonators. Opamps of high speed consume more power than those of low speed, and this is one of the reasons why high speed sigma-delta ADCs using resonators consume a lot of power.